<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>样式的演示</title>
</head>
    <style>
        .top{
            border: 1px solid red ;
            width: 60%;
            height: 500px;
            margin: auto;
        }
    </style>
<body>
    <div class ="top">我想</div>
</body>
</html>